SUMMARY. Smoking is a pressing public health problem for American Indians (AI) and is a major contributor to disparities in cancer mortality. Increasingly, adults who smoke are also using electronic cigarettes (e-cigs), either as an aid for smoking cessation or to reduce smoking. Very little has been reported about e-cig use, or ?vaping?, among AI despite the burgeoning use of these products nationwide. The Specific Aims of our project are to: 1. Describe baseline prevalence and patterns of e-cig use among adult AI smokers in the Cherokee Nation, including reasons for e-cig use such as desire to quit smoking, duration and intensity of e-cig use, preferred nicotine concentration, flavors, and vapor device characteristics. Hypothesis: Vaping will be more common than reported in other smoking populations. 2. Assess baseline characteristics associated with dual use of e-cigs and smoking. Hypotheses: E-cig users will be younger, more often female, more desirous of quitting smoking, and use fewer cigarettes per day than non-users. Prevalence of vaping will not differ by level of nicotine dependence. 3. Examine whether baseline biomarkers of tobacco constituents differ between dual users of e-cigs and cigarettes compared to cigarette-only users. An exploratory sub-aim is to assess the feasibility of urine collection to measure NNAL on a subsample of participants. Hypotheses: The degree of constituent exposure will be directly associated with degree of e-cig substitution for cigarettes. Greater substitution will confer lower levels of exposure to the toxicant carbon monoxide, with no difference in markers of nicotine. 4. Reassess vaping and smoking after 18 months. Hypotheses: The prevalence of use of e-cigs will increase over time. Use of e-cigs will predict the following outcomes at 18 months: fewer cigarettes smoked per day, less nicotine dependence, lower levels of harmful constituents, but not smoking cessation. This proposed research project explores dual use of electronic cigarettes and combustible cigarettes among American Indians (AI) in the context of three overarching goals related to the P20 Cherokee Nation/Stephenson Cancer Center Collaborative on Cancer Disparities Research: 1) to address current gaps in our understanding of the use of e-cigs among AI smokers; 2) to increase the research skills and expertise of two AI emerging investigators, one at the Cherokee Nation and one at the Stephenson Cancer Center; and 3) to build an enduring collaborative research relationship between the Cherokee Nation and Stephenson Cancer Center for future NCI sponsored studies addressing tobacco-related cancer among AI. This work is innovative because it will capture in real time the evolving impact of e-cigs on smoking and markers of toxicant exposure and nicotine addiction in a high risk population. This work is translational, as many U.S. communities, regardless of racial composition, face high rates of smoking and rising use of e-cigs.